1. Technical Field
The present invention relates to a virtual image display device such as a head-mounted display mounted on a head.
2. Related Art
Recently, as virtual image display devices that enable formation and observation of virtual images like head-mounted displays, various devices of a type of guiding image light from a display element to eyes of an observer using a light guide plate have been proposed (see Patent Document (JP-A-2008-172367) and Patent Document 2 (JP-A-2000-249969)).
Not only in the cases of Patent Documents 1 and 2, but many head-mounted displays generally have shapes like spectacles and sunglasses in view of downsizing and design of the devices. In the head-mounted display having the configuration, when image light is propagated along the shape, the image light is output with a direction of a center optical axis as the center thereof at nearly horizontal zero degrees. The observer continues to observe images while keeping the eyes straight ahead so that the direction of eyes may be the direction of the center optical axis of the image light.
However, the human eye has a structure of opening wide for observation in the state in which the observer looks straight ahead, and the eyelids of the observer take heavy strain. Therefore, when the state continues in a long period, the observer feels stress due to eyestrain. The head-mounted displays are intended for continuous use in long periods, such stress may be particularly problematic.